More from NBC

Polar bears on thin ice?

A grim future for polar bears is one of the most tangible and poignant outcomes of global warming. Four years ago, federal researchers reported that two-thirds of the world's polar bear habitat could vanish by mid-century. Other experts foresee an irreversible ice-free Arctic in the next few years as more likely.

The new study, which challenges the idea of a tipping point, says rapid ice loss could still happen, but there's a chance that the threatened bears aren't quite doomed.